a dashboard screen showing current CO₂ levels in ppm (parts per million) for 15 rooms / spaces at the Chaos Computer Club’s 39C3 conference the levels are illustrated with tachometer-style indicators that are colour-coded using standard green (good) -> yellow (medium) -> red (bad) colour scheme correlating with the ppm measured in each room the raw ppm value for each room is also visible in the middle of its respective “tachometer”